Various bacteria and molds occur in our life space. These microorganisms often spoil foods or cause the generation of an offensive odor, offending us. Further, these microorganisms can cause diseases such as food poisoning or dermatopathy such as ringworm on the human body. Thus, the inhibition of proliferation of microorganism is an important subject for sanitary and comfortable life. It has been desired to provide our personal effects such as medical goods, daily necessaries and clothing with antibacterial capacity.
As a material of medical goods, daily necessaries, clothing, etc. there is used by preference a synthetic resin, which is light and rigid and can be freely molded to a desired shape. However, most synthetic resins have no antibacterial capacity themselves. In recent years, studies have been made on methods for imparting antibacterial function to synthetic resin-molded articles.
As a method for obtaining a synthetic resin-molded article having antibacterial capacity (hereinafter referred to as "antibacterial resin-molded article") there is disclosed a method of incorporating metals such as silver, copper and zinc in a synthetic resin in JP-A-54-147220 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"). Further, JP-A-59-133235 discloses a method of incorporating a particulate zeolite-based solid matter ion-exchanged with silver ion or copper ion in a synthetic resin.
However, the antibacterial resin-molded article obtained by the method involving the incorporation of a metal-containing compound is disadvantageous in that it is liable to discoloration due to the metal compound incorporated therein and thus exhibits impaired external appearance and commercial value. Further, the antibacterial resin-molded article obtained by the method involving the incorporation of a particulate ion-exchanged zeolite-based solid matter in a synthetic resin is liable to production of chlorides by the reaction of metallic ions such as silver ion and copper ion with chlorine ion, if any, making it impossible to obtain a sufficient antibacterial capacity.
On the other hand, there is a method involving the incorporation of an antibacterial natural material which is little harm to the human body in a synthetic resin. Examples of such an antibacterial natural material include allyl isothiocyanate extracted from mustard or Japanese horse radish, protamine extracted from mature testis of salmon, trout, etc., and .epsilon.PL obtained from microorganism belonging to streptomyces. A technique for the incorporation of a natural polylysine compound in a textile product is described in, e.g., JP-A-8-170217.
However, allyl isothiocyanate is disadvantageous in that it can vaporize readily during the molding of a resin composition and hence must be used in a large amount to render the resulting antibacterial resin-molded article fully antibacterial. Further, protamine is disadvantageous in that it is a protein and hence can be affected by heat too easily to withstand the processing temperature of the resin composition.
Among these natural antibacterial agents, .epsilon.PL can exert an excellent antibacterial effect even when used in a small amount. Further, .epsilon.PL can maintain its antibacterial effect even when heated to a temperature of from 200.degree. C. to 250.degree. C., which is required in the molding of a synthetic resin. .epsilon.PL is normally used in the form of liquid composition obtained by mixing with ethanol as disclosed in JP-A-2-20271, liquid composition obtained by mixing with acetic acid as disclosed in JP-A-4-53475, powdery composition obtained by mixing an amino acid such as glycine as disclosed in JP-A-5-68520 or commercially available powdery composition obtained by mixing dextrin.
However, if such a composition is incorporated in a synthetic resin before molding to provide a resin-molded article with an antibacterial capacity, the resulting resin-molded article is liable to foaming.due to evaporation of solvent or burning of ingredients other than .epsilon.PL, impairing the external appearance of the molded article or damaging the mold or roll. Further, .epsilon.PL can be hardly dispersed uniformly in a resin, occasionally making it impossible to provide a sufficient antibacterial effect. Moreover, if the resin-molded article is adapted for use in environments requiring cleaning resistance, it is necessary to incorporate .epsilon.PL in the resin in a high concentration, adding to the production cost.
Further, .epsilon.PL is a substance having a high hydrophilicity and thus can be hardly dehydrated or dried. Therefore, normally available .epsilon.PL has a high water content.
In general, .epsilon.PL is mainly used as food additives or the like because of its effect. In these fields, the water content in .epsilon.PL offers no special problem. In the previously mentioned field requiring the provision of a synthetic resin with an antibacterial capacity, however, the water content contained in .epsilon.PL has an adverse effect on the moldability of the resin, causing molding defects or deterioration of the external appearance of the molded article. In particular, .epsilon.PL having a high water content cannot be uniformly dispersed in a coating compound such as oil-based coating compound and printing ink. Further, such a coating compound or printing ink cannot be properly dried. Moreover, the resulting coat or printed matter exhibits an ill-developed color or a poor external coating or printing appearance.